Homogeneous reactions catalysed by transition metals, allowing formation of carbon-carbon bonds, are considered to be important synthetic methods. One example thereof is the olefin metathesis reaction, which has proved its efficiency in the synthesis of high-molecular-weight polymers as well as the synthesis of medicines or other materials. Metal alkylidene complexes, notably molybdenum complexes, have shown good activities in homogeneous olefin metathesis reactions, even in the presence of various functional groups, and these performances greatly depend on the other ligands present around the metal. By way of example, R. R. Schrock's work can be mentioned, who compared the activities of many molybdenum and tungsten imidocarb complexes for the homometathesis of 1-octene (Organometallics, 2009, 28 (1), 355-360).
Despite these advantages, these catalysts are likely to deactivate by interaction of the organometallic species in solution, via polynuclear species formation or dismutation mechanisms. These interactions are favoured by the absence of repulsion between the metal centers, as described by R. R. Schrock for tungsten complexes (Chem. Rev., 2009, 109, 3211-3226). Besides, recycling homogeneous catalysts and/or separating them from the reaction products are generally delicate aspects of homogenous processes.
Surface organometallic chemistry has been developed to overcome these drawbacks, Homogeneous catalysts grafted on an oxide surface are recyclable and the metal centers anchored to the surface are not likely to interact with one another. However, this methodology suffers from the heterogeneity of the surface sites of a solid, which leads to a multiplicity of active sites. It is furthermore difficult to control the metal content of the solid obtained or to modify the environment of the metal so as to vary its catalysis properties.
We have discovered that grafting organometallic compounds on an anion by means of at least one covalent metal-oxygen bond allows to overcome these limitations. The species formed thus has an anionic character, which affords several advantages:                the interactions between metal centers in solution are thus reduced, due to the repulsion of the charges, and        the entity formed is soluble in ionic solvents, which opens up the possibility of its immobilization and recycling in a two-phase technology.        